Telephone system



March 13, 1934. R. G. RICHARDSON TELEPHONE SYSTEM Filed NOV. 50, 1931 Fem SE'BAN/(s Rodney G. Eichardscm Patented Mar. 13, 1934 l STATES 1,951,109 TELEPHONE SYSTEM Rodney G. Richardson,

mesne assignments, to

oratories, Inc., Chicago,

Delaware Chicago, Ill., assignor, by

Associated Electric Lab- Ill., a corporation of Application November 30, 1931, Serial No. 577,967

20 Claims.

This invention relates to telephone systems, and its object is to improve two-way trunks that are arranged to be automatically seized or connected with at either end.

Two-way trunks of the above type are arranged so that they will be automatically marked busy or guarded at both ends when seized at either end in order to prevent simultaneous seizure in two connections. The most commonly used trunkbusying arrangement involves the operation of the line and release relays of an outgoing repeater and the operation of the line and release relays of an incoming switch. With this arrangement, the distant end of the trunk is guarded only after the four relays mentioned have been operated. There is, therefore, a considerable interval after the seizure of a trunk during which the distant end is unguarded and therefore subject to seizure at that point. Numerous attempts to overcome this dilculty have resulted in a reduction of the number of intervening relay operations between seizure and guarding, but, insofar as applicant is aware, none of the prior arrangements have completely eliminated the unguarded interval.

According to the present invention, a trunk is marked busy without any intervening relay operation upon its seizure at either end. This instantaneous busying arrangement constitutes one of the main features of the invention.

Another feature of the invention is the arrangement for preparing the trunk switch for operation over a circuit which includes only one trunk conductor. This arrangement frees the other trunk conductor for use in the guarding circuit.

The foregoing features and others not specically mentioned will be discussed in more detail hereinafter, reference being had to the accompanying single figure of drawing. The invention is illustrated in the drawing by a two-way trunk connecting two automatic telephone exchanges. Repeater R and selector S are associated with the trunk in one exchange, and repeater Rl and selector S1 are associated with the trunk at the other exchange. Repeaters R and R1 are of the type commonly used in two-wire automatic telephone systems with such modications as are required by the present invention.

The local trunks terminating in the repeaters are accessible in the banks of selectors in their respective exchanges. Selectors S and Sl are ordinary Strowger type selector switches modified to operate in a system employing the invention.

These selectors, together with local selectors of the same rank, have access to other local selectors or connectors in the respective exchanges.

Before proceeding with a detailed description of the invention, the operation of an ordinary selector switch in seizing an idle trunk will be discussed briey. v The test circuit of the ordinary selector is exactly the same as that of selector S shown in the drawing. After being directively operated to the required level, the switch wipers, in the well-known manner, are rotated in search 6 of an idle trunk. When an idle trunk is found, the switching relay corresponding to relay 25 of selector S operates and switches the calling line from the line relay to the talking wipers of the switch. The test Wiper is switched from the lower terminal to the upper terminal of the switching relay, the latter terminal being grounded by the release relay of the switch during the operation and for an interval after the seizure of the idle trunk. The test wiper accordingly applies ground to the test contact and release trunk conductor of the seized trunk, thereby guarding the same until the release relay of the succeeding switch applies ground to the release trunk conductor.

Assuming that a connection has been extended by way of an ordinary selector to the trunk line comprising conductors 18-20 terminating in repeater R, the calling line is extended over conductors 18 and 20, reversing contacts of relay 3 85 and the upper and lower windings oi relay 4 to battery and ground. Ground on the test wiper of the seizing switch is extended over release trunk conductor 19, contacts 41 and 50, conductor 22, trunk conductor 2, contacts 63, conductor 61, and contacts 87 and 85 to release trunk conductor 57 of the trunk terminating in repeater R1. As ground is applied to the release trunk conductor of repeater R1 imrnediately upon the seizure of the trunk incoming to repeater R, the trunk is therefore guarded against seizure at the distant end until such time as the usual guarding circuit is completed.

Referring to repeater R, relay 4 operates over the loop of the calling line, completes a circuit for relay 5 at contacts 7 and completes a circuit at contacts 9 for preparing the incoming selector S1 for operation. The latter circuit extends from grounded trunk conductor 2, oo ntacts 9, upper winding of polarized relay 3, contacts 16, trunk conductor 1, contacts 64 and 68, conductor 62, contacts 92, upper winding of relay '75 to battery. Relay '75 operates and completes a circuit for relay 76 at contacts 83. Release relay 5 of repeater R operates over its pre- 110 viously traced circuit and applies ground to release trunk conductor 19 to hold up the preceding switches after the ground is removed from this conductor at the preceding switch. Line relay 29 of selector S is disconnected from trunk conductor 1 at contacts 11, and an operating circuit is completed for this relay at contacts l2. A circuit is prepared for relay 6 at contacts 13, a circuit is completed for the polarizing Winding of relay 3 at contacts 14, and release trunk conductor 19 is disconnected from trunk conductor 2 at contacts l5. At the same time that relay 5 operates, we find that rela-y 76 of selector S1 also operates and connects the lower Winding of line relay 75 to trunk conductor 2 by way or" contacts and 98, conductor 59, and contacts 71. Relay now remains operated over the loop including the uppei` winding of polarized relay 3. Relay 76 disconnects release trunk conductor 57 from trunk conductor 2 at contact 85, and contacts 1GO apply ground thereto to guard the trunk throughout the connection. The further circuits closed by relay 76, including the impulsing circuit and the local holding circuit, are the same as for an ordinary selector. In selector S, relay 29 is operated over the circuit completed by relay 5, and this relay in turn completes a circuit for relay 28. Relay 28 operates, opens the connection between release trunk conductor 19 and trunk conductor 2 at contacts 41, and completes Various other circuits which are of no utility in the present conne"- tion. Relay 3 of repeater R is not operated at this time, as the current flow in the two windings is in a direction such that the two windings oppose each other.

The calling subscriber now dials a digit of the called number, and the circuit of relay 4 is opened intermittently. Each time relay 4 restores, a circuit is completed for relay 6 at contacts 8, and the circuit for relay 75 is opened at contacts 9. Relay 6, which is slow-releasing, operates in response to the rst impulse and remains operated throughout the series of impulses, completing a low-resistance impulsing path independent of relay 3 by closing contacts 17. Relay 75 responds to the interruptions of its circuit at contacts 9 and transmits a series of impulses to vertical magnet in series with relay 77 by intermittently closing contacts 84. Magnet 80 responds in the usual manner'and raises the switch wipers to the called level. Relay 77 operates in series with the vertical magnet and, as soon as the switch steps oil normal, completes a circuit for relay 78 by way or" contacts 86 and 88, interruptor contacts of the rotary magnetv and the oil-normal contacts. Relay 78 completes a locking circuit for itself at contacts and prepares a circuit for the rotary magnet at contacts 91. When relay 77 restores shortly after the last impulse of the series, the usual operating circuit for the rotary magnet is closed, and the magnet steps the switch wipers in on the first set of contacts in the called level. The rotary magnet opens the circuit of relay 78, and this relay restores. The switch then tests for an idle trunk in the usual manner, and, when such a trunk is found, relay 79 operates and extends the calling loop ahead to the next switch of the train. A point in the circuit connecting trunk conductor 2 'and release trunk conductor 57 is opened at contact 87 so that, upon the release of relay 76, the two conductors will not again be joined until the connection is released. When relay 76 nnally restores shortly after the trunk ahead has been seized, the repeater Rl is marked busy by ground on release trunk conduct-or 57 by way of contacts 85 and 99. The trunk is thereby guarded against seizure until the connection is released.

When the calling subscriber hangs up, the final switch of the train releases and disconnects the holding ground from the release trunk conductor, thereby permitting the relay 79 of selector Sl to restore. Relay 79 removes ground from release trunk conductor 67 and re-connects this conductor to trunk conductor 2 to make the original busying circuit again operative.

In case the inter-oiice trunk is initially seized at the exchange at which repeater R1 is'located, we have the following operation: Upon the seizure oi the trunk, the calling line is extended over conductors 56 and 58 and the reversing contacts of relay 55 to line relay 54. Ground on the test wiper of the seizing switch is extended over conductor 57, contacts 85 and 87, conductor 61, contacts 3, trunk conductor 2, conductor 22, contacts 5o and 41, and conductor 19 to the test contact of the trunk comprising conductors l8-29. This latter trunk is accordingly guarded instantaneously when the opposite end of the inter-oflice trunk is seized. Line relay 54 operates and completes a circuit for relay 53. Relay 53 completes a circuit for slow-to-operate relay 51 at contacts 7G and disconnects the upper winding of line relay 75 from trunk conductor 1 at contacts 68. During the interval required for relay 51 to operate, ground is applied from conductor 2, contacts 74, upper winding of polarized relay 55, contacts 66 and 64, trunk conductor 1, contacts 11, conductor 21, contacts 30, to the upper winding of line relay 29 of selector Sl. Relay 29 operates and completes the usual circuit for relay 28. Relay 28 operates and at contact 23 connects the lower winding of relay 29 to trunk conductor 2, so that the relay will hold up over two windings in series after ground is removed from conductor 2 by the operation of relay 51. Relay 28 of selector S also opens the circuit connecting release trunk conductor 19 with trunk conductor 2 by opening contacts 41, and applies ground directly'to conductor 19 at contacts 40. The subscriber dials and the impulses are repeated over the trunk in the usual manner to step the wipers of selector S to the called level. The selector then hunts for and connects with an idle trunk in the usual manner, and upon relay 25 operating a further point in the circuit connecting conductors 19 and 2 is opened at contacts llol 50; and ground is connected up at contacts 44 'r so that upon the release of relay 28 it will be applied by way of contacts 41 to conductor 19 as long as the connection is maintained. The release of the switches in this connection is substantially the same as that previously described for the iirst connection.

What is claimed is:

1. In a telephone system, a two-conductor trunk, means for seizing the trunk at either end,

said inea-ns marking both ends of the trunk busy instantaneously upon the seizure of either end.

2. In a telephone system, a two-conductor trunk connecting two exchanges, a source of guarding potential at one exchange, a test contact for the trunk at the other exchange, means for seizing the trunk at said one exchange, said means connecting said source to said contact over'the trunk.

3. In a telephone system, a two-conductor trunk, a test contact for each end of the trunk, l

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means for seizing the trunk at either end, a source of guarding potential, said means simultaneously connecting said source to the contacts at each end of the trunk.

4. In a telephone system, a trunk line including two talking conductors, a test contact for end of the trunk line, and a direct connection between the contacts at each end of the trunk including a talking conductor 01"' the trunk.

5. In a telephone system, a trunk including two talking conductors, a branch including two talking conductors and a test conductor at each end of the trunk, and circuit connections directly connecting the test conductors of said branches via a talking conductor of the trunk.

6. In a telephone system, a trunk including two talking conductors, a branch including two talking conductors a test conductor at each end of the trunk, means for extending a connection to the truck via either branch, said means also applying a guarding potential to the test conductoi` oi the branch connected with immediately on the completion of the connection, and normal circuit connections directly connecting both said test conductors.

'7. In a telephone system, a trunk including two talking conductors, means for seizing the trunk at either end, circuit connections including a talking conductor of the trunk, said means also initially guarding the trunk against seizure at one end over said circuit connections after it is seized at the other end, and other circuit connections operated responsive tc said seizure or maintaining the trunk guarded against seizure at said one end while freeing said trunk conductor for other use.

8. In a telephone system, a trunk including two talking conductors, a branch including two talking conductors and a test conductor at each end of the trunk, circuit connections direciy connecting the test conductors of said branches via a talking conductor of the trunk while the trunk is idle, and means for disconnecting said test conductors responsive to the trunk being taken into use.

9. In a telephone system, a trunk including two talking conductors, a branch including two talking conductors and a test conductor at each end of the trunk, circuit connections connecting the test conductors of said branches via a talking conductor of the trunk, and means for disconnecting said test conductors and for connecting the talking conductors of said branches via the talking conductors or" the trunk.

lo. In a telephone system, a two-way trunk. a relay connected to each end of the trunk, means for seizing the trunk at either end, means for operating the relay at one end responsive to the seizure of the trunk at the other end, means controlled by the operated relay for guarding the trunk against seizure at said one end, and means for guarding the trunk against seizure at said one end the interval between the seizure at the other end and the completion of the operation of said relay.

ll. In a telephone system, a trunk including two talking conductors adapted to be connected with at either end, a relay at one end or the trunk, means for extending a connection to the other of the trunk, and means responsive to said connection ior operating said relay over a circuit including c-ne oi said trunk conductors and icr guarding the trunk against seizure at said one end over a circuit including the other of said trunk conductors.

12. In a telephone system, an automatic switch,

a trunk including two talking conductors, a double-wound impulse relay for the switch having one winding connected to one of said trunk conductors, a guarding conductor for the switch normally connected to the other of said trunk conductors, and means controlled by said relay for disconnecting said other trunk conductor from said guarding conductor and for connecting it to the other winding of said relay.

13. In a telephone system, an automatic switch, a trunk including two talking conductors, a double-wound impulse relay for the switch having one winding normally connected to one trunk conductor, a guarding conductor for the switch normally connected to the other trunk conductor, means controlled by said relay for setting the switch, means for disconnecting said other trunk conductor from the guarding conductor and for connecting it to the other winding of said relay during the setting of the switch, and means for disconnecting both of said trunk conductors from the windings of said relay and for maintaining the separation of the guarding conductor and said other trunk conductor responsive to the completion of the setting of the switch.

le. In a telephone system, a trunk connecting two exchanges, a test contact for the trunk at one exchange, means for connecting with the trunk at the other exchange, said means also connecting guarding potential to said contact over the trunk. l5. In a telephone system, a trunk connecting two exchanges, a test contact for the trunk at each exchange, and a metallic circuit normally connecting said contacts.

16. In a telephone system, two exchanges, a test contact for the trunk at each exchange, a direct metallic connection between said contacts, means for taking the trunk into use, and means for opening the connection between said contacts after the trunk is taken into use.

17. In a telephone system, a trunk including talking conductors connecting two exchanges, a test contact for the trunk at each exchange, and a metallic circuit including one of the talking conductors of the trunk directly connecting said contacts while the trunk is idle.

18. In a telephone system, a trunk connecting two exchanges, a test contact for the trunk at one exchange, means for trunk at the other exchange, means responsive to said connection for temporarily applying a guarding potential to said contact from said other exchange, and means further responsive to said connection for subsequently applying a guarding potential to said contact from said one exchange.

19. In a telephone system, a trunk, a line relay and a test contact at one end of the trunk, means controlled by said relay for applying a guarding potential to said contact, means trunk at the other end thereof to operate said relay, and means for applying a guarding potential to said contact during the interval between the seizure of the trunk and the operation of said relay.

20. In a telephone system, a trunk, a test contact associated with one end of the trunk, means for seizing the trunk at the other end, means eieotive for instantaneously applying a temporary guarding potential to said Contact upon the seizure of the trunk, and means including a relay operated responsive to said seizure for replacing said temporary guarding potential with a permanent guarding potential.

RODNEY G. RICHARDSON.

a trunk connecting connecting with the for seizing the llo 'lid 

